For a number of years, a need has been recognized for vehicle simulators that can be operated by a driver manipulating conventional controls to be shown the results of his action as by a simulated display. For example in training activities, simulators are widely used with respect to airplanes, helicopters and ground vehicles. In addition to training uses, vehicle simulators have been found useful in test and design work.
In the current state of technology, a visual display is considered a necessary component of a vehicle simulator. Accordingly, as the pilot or driver of a simulated vehicle manipulates the controls, he is provided with a responsive display showing the driver's view as the vehicle simulates movement in a programmed environment. Contemporary simulators utilize computer graphics techniques to provide a dynamic display. An environment is programmed and positional signals are developed to indicate the position and orientation of the vehicle in the environment. Representative simulator data is then supplied to a computer graphics system to attain a dynamic display.
Typically, the operation of the computer graphics system to provide image display signals from simulator data involves a relatively large time delay that often presents a problem. Consider an example. A high performance automobile may respond to the controls with a delay of only thirty milliseconds (30 ms). Simulator models for such an automobile are capable of approaching such response times in providing simulator electrical signals to indicate the position and orientation of the car. However, the utilization of such simulator signals by a computer graphics system (image generator) to provide signals for a visual display is likely to take much longer, e.g. sixty milliseconds (60 ms). Thus, accepting the inherent delay of the qraphics system introduces a response delay that is intolerable for many simulator applications.
Techniques have been used in previous vehicle simulators to compensate for the delay of the graphics system or image generator. Generally, the compensation has involved extrapolating from the current motion of the vehicle to predict future positional data for the display. Specifically, polynomial extrapolation, as well as feedback techniques and moving average techniques have been proposed for compensating time delays in prior systems. However, such arrangements tend to be inaccurate and typically impose the limitation that linear dynamics models be employed in the system. Because vehicle dynamics are not linear, in some instances a severe constraint is imposed on model fidelity if operation is restricted to motion extrapolation or linear prediction. Accordingly, a need exists for an improved vehicle simulation system that is relatively economical, enables the use of non-linearity in models and enables realistic time approximation of the motion characteristics of an actual vehicle.
In general, the system of the present invention incorporates simultaneous separate, but coordinated, dynamics models, each performing a specialized function in real time. In accordance with the invention, nonlinearity can be built into the models as needed. At least one simulation model simulates the complete vehicle movement to provide reference positional signals indicative of current position and orientation. As disclosed, the prediction model in the system utilizes the positional reference signals from the simulation model along with extrapolation representations (solely from control actions) to predict the positional state of the vehicle at a time approximating the time of display. In the disclosed embodiment, model fidelity is insured by periodically updating predictions with initial reference conditions provided from a full chassis simulation model. Also, in the disclosed embodiment, the simulation model involves two separate units, one in the form of a nonlinear suspension unit with relatively large bandwidth for full road and handling inputs. The other unit is the nonlinear full vehicle dynamics model with some or all of the nonlinear effects simulated.